按值对行进行分组和计数，直到它发生变化

Question

我有一个 table 消息在发生时存储在其中。通常有一条消息 'A'，有时 A 由一条消息 'B' 分隔。现在我想对值进行分组，以便能够分析它们，例如找到最长的 'A'-streaks 或 'A'-streaks 的分布。

我已经尝试过 COUNT-OVER 查询，但每条消息都会继续计数。

SELECT message, COUNT(*) OVER (ORDER BY Timestamp RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)

这是我的示例数据：

Timestamp        Message
20150329 00:00   A
20150329 00:01   A
20150329 00:02   B
20150329 00:03   A
20150329 00:04   A
20150329 00:05   A
20150329 00:06   B

我想要以下输出

Message    COUNT
A          2
B          1
A          3
B          1

Answer 1

这很有趣:)

;WITH cte as (
SELECT Messages.Message, Timestamp, 
ROW_NUMBER() OVER(PARTITION BY Message ORDER BY Timestamp) AS gn,
ROW_NUMBER() OVER (ORDER BY Timestamp) AS rn
FROM Messages
), cte2 AS (
SELECT Message, Timestamp, gn, rn, gn - rn  as gb
FROM cte 
), cte3 AS (
SELECT Message, MIN(Timestamp) As Ts, COUNT(1) as Cnt
FROM cte2
GROUP BY Message, gb)
SELECT Message, Cnt FROM cte3
ORDER BY Ts

这是结果集：

  Message   Cnt
    A   2
    B   1
    A   3
    B   1

查询可能更短，但我 post 这样做是为了让您了解发生了什么。结果完全符合要求。这是最重要的部分 gn - rn 这个想法是对每个分区中的行进行编号，同时对整个集合中的行进行编号，然后如果你从另一个中减去一个，你将得到 'rank' 每组。

;WITH cte as (
SELECT Messages.Message, Timestamp, 
ROW_NUMBER() OVER(PARTITION BY Message ORDER BY Timestamp) AS gn,
ROW_NUMBER() OVER (ORDER BY Timestamp) AS rn
FROM Messages
), cte2 AS (
SELECT Message, Timestamp, gn, rn, gn - rn  as gb
FROM cte 
)
SELECT * FROM cte2

Message Timestamp           gn  rn  gb
A   2015-03-29 00:00:00.000 1   1   0
A   2015-03-29 00:01:00.000 2   2   0
B   2015-03-29 00:02:00.000 1   3   -2
A   2015-03-29 00:03:00.000 3   4   -1
A   2015-03-29 00:04:00.000 4   5   -1
A   2015-03-29 00:05:00.000 5   6   -1
B   2015-03-29 00:06:00.000 2   7   -5

Answer 2

这里有一个更小的解决方案：

DECLARE @t TABLE ( d DATE, m CHAR(1) )

INSERT  INTO @t
VALUES  ( '20150301', 'A' ),
        ( '20150302', 'A' ),
        ( '20150303', 'B' ),
        ( '20150304', 'A' ),
        ( '20150305', 'A' ),
        ( '20150306', 'A' ),
        ( '20150307', 'B' );

WITH 
c1 AS(SELECT d, m, IIF(LAG(m, 1, m) OVER(ORDER BY d) = m, 0, 1) AS n FROM @t),
c2 AS(SELECT m, SUM(n) OVER(ORDER BY d) AS n FROM c1) 
    SELECT m, COUNT(*) AS c
    FROM c2
    GROUP BY m, n

输出：

m   c
A   2
B   1
A   3
B   1

想法是在消息更改的行处获取值 1：

2015-03-01  A   0
2015-03-02  A   0
2015-03-03  B   1
2015-03-04  A   1
2015-03-05  A   0
2015-03-06  A   0
2015-03-07  B   1

第二步只是当前行值 + 所有前面值的总和：

2015-03-01  A   0
2015-03-02  A   0
2015-03-03  B   1
2015-03-04  A   2
2015-03-05  A   2
2015-03-06  A   2
2015-03-07  B   3

这样您就可以按消息列和计算列获得分组集。

按值对行进行分组和计数，直到它发生变化

Grouping and counting rows by value until it changes

sql

sql-server-2014